Steam Gifts is buggy when it comes to DLC; I own this but it still lets me enter. (Although I won't.) I doubt you could activate or receive it without owning the game.

This DLC is also kind of something you're better off without...it just drops a bunch of boring, overpowered (for early game) gear in your inventory right after character creation. But oh well, it's still generous of hilmarillon to give it away.